The invention is particularly well suited for use in a ring-piston accumulator method of forming a multi-layer parison which is utilized in the production of, for example, automotive fuel tanks and other containers which are desirably produced from laminates of dissimilar materials, e.g. an outer wall composed of a high molecular weight polyethylene and an inner wall composed of a barrier-type resin, such as polyamide.
U.S. Pat. No. 2,710,987 is typical of the many patents relating to the continuous extrusion of plastic articles of different laminates. U.S. Pat. No. 3,266,093 discloses the use of an inlet relatively near the discharge outlet of a continuous extrusion device, as a means of adding an outer laminate to the material being extruded. However, the devices of these patents do not utilize a ring-piston to force the resinous material from an accumulation chamber into an adjacent mold. It can be appreciated from a study of these patents that the different resinous materials are thermally separated until just prior to their movement into a mold in which the article is formed. U.S. Pat. No. 4,120,633 is directed to an extrusion device which employs an accumulation chamber and ring piston in the production of a multi-layer parison. In this device, however, the laminates of plastic material are all forced into the accumulation from inlets which are located above the accumulation chamber. The invention is directed to a ring piston-type extrusion device, wherein at least one of the inlets for a laminate is located, so that the laminate flowing therethrough into the device will not contribute to the forces which cause movement of the ring-piston to a retracted position out of the accumulation chamber, to insure that the laminate will be uneffected and not distorted in any way be such forces, as may be the case when several laminates combine to exert force against the ring piston to move it to its retracted position above the accumulation chamber.
Briefly stated, the invention is in an apparatus for forming a multi-layer parison of different resinous materials. The apparatus comprises an annular accumulation chamber which is designed to receive and hold at least one of the two different resinous materials. The chamber has a longitudinal axis which is, normally, vertically disposed when the apparatus is in operation and which is spaced from an annular discharge orifice through which the extrudite exits the apparatus into an adjacent mold. The orifices and chamber are connected by a discharge passageway. A special annular opening is provided in the discharge passageway vertically below the chamber. Means are provided for moving into the chamber, under pressure, one of the different resinous materials until the chamber is filled to a desired level. A single, annular ring-piston or ram is disposed in the chamber and movable axially thereof to force this resinous material from the chamber through the discharge passageway and orifice into an adjacent mold in which the parison and resulting product are formed. Means are supplied for forcing the other of the different resinous materials through the entrance opening into the discharge passageway at the same time as the first resinous material is being forced from the chamber to produce within the discharge passageway at least two laminates of different resinous materials for subsequent passage through the orifice into a mold which is connected to the orifice.
Another feature of the invention is the utilization of the entrance opening in the discharge passageway as the sole inlet through which resinous material is forced into the accumulation chamber for subsequent discharge through the discharge passageway and orifice as a single laminate or layer of material.